This invention relates to medical diagnostic apparatus. More specifically, the invention relates to a flexible patient transfer cradle. The preferred embodiment of the cradle is disclosed herein, by way of example, with reference to nuclear magnetic resonance (NMR) apparatus.
A whole-body NMR system typically comprises a magnet, and a mobile patient support table capable of being secured to the magnet by means of a docking mechanism. In the preferred embodiment, the magnet is of superconductive construction configured as a solenoid having a longitudinal bore aproximately 90 cm. in diameter. Useful bore diameter for accommodating a patient is reduced to approximately 55 cm. by gradient, shim, and radio-frequency coil assemblies which are installed within the bore. A patient transfer cradle equipped with a plurality of wheels is provided to retrievably translate the patient, initially positioned atop the patient support table, into the magnet bore which has a bridge structure to support the weight of the cradle and the patient. A track fabricated on the bridge and top of support table engages bearings located on either side of a longitudinal groove formed on the underside of the patient cradle to guide the latter in its translational movement into and out of the bore. In a typical NMR system utilizing a 1.5 Tesla superconductive magnet, the total cradle travel range is approximately 300 cm. The cradle is designed to support a 300 lb. patient.
A problem experienced with conventional rigid cradles is the tendency of such cradles to wobble on two wheels when rolling on an unlevel support table or bridge surface. In use, the repeated transfer of the patient weight from 16 wheels in a typical cradle to 2 tends to cause premature failure of plastic ball bearings.
Another problem associated with cradles of conventional rigid design is the tendency of such cradles to move very roughly over small gaps and inclines. One such gap, transverse to the direction of travel, is between the bridge structure and the support table. Because cradle structure is rigid, each set of wheels is more likely to transmit to the patient mechanical shock due to such discontinuities. As a result, patient comfort is reduced.
It is, therefore, a principal object of the invention to provide a flexible patient transfer cradle capable of smooth movement on surfaces having irregularities.
It is a further object of the invention to provide a flexible patient transfer cradle which uniformly distributes the patient load to the roller bearings.
It is another object of the invention to provide a flexible patient transfer cradle which enhances patient comfort.